The present invention relates to a semiconductor device manufactured by using a thin film transistor (hereinafter, referred to as a TFT), utilizing a semiconductor film, and a method of manufacturing the same. In particular, the present invention provides a technique that is preferably applicable to an electro-optical device typified by a liquid crystal display device and an electronic device equipped with such an electro-optical device. In this specification, a semiconductor device generally refers to devices that function by utilizing semiconductor characteristics, and also includes the above-mentioned electro-optical device and electronic device equipped with the same.
A liquid crystal display device is utilized for displaying an image and character information in a notebook personal computer (notebook computer) and a portable information terminal. Compared with a passive liquid crystal display device, an active matrix liquid crystal display device allows a high-precision image to be obtained, so that the latter is being preferably used for this purpose. In the active matrix liquid crystal display device, TFTs that are active elements are arranged in a matrix so as to correspond to respective pixels in a pixel portion. As a TFT, an n-channel TFT is typically used, and the TFT functions as a switching element to control a voltage applied to liquid crystal on a pixel basis, thereby conducting a desired display of an image.
According to a technique of manufacturing a TFT with an amorphous semiconductor typified by amorphous silicon, the TFT can be formed on a substrate with a large area at a low temperature of 300xc2x0 C. or lower, so that the amorphous semiconductor is considered as a material suitable for mass-production. However, the TFT in which an active layer is formed of amorphous silicon has a small field-effect mobility, i.e., a value of 1 cm2/Vsec or more cannot be obtained. Therefore, such a TFT is utilized specifically for a switching element provided in a pixel portion.
Such an active matrix liquid crystal display device is used in a wide range of applications such as a liquid crystal TV receiver as well as a portable information terminal and a notebook computer, and in order to achieve an increased area size of a screen and enhancement of an image quality, there is an increased demand for high precision and a high opening ratio.
The active matrix liquid crystal display device is manufactured by using a plurality of photomasks in a light exposure process, so as to dispose a gate wiring, a data wiring, a pixel electrode, and the like with good precision in a stacked manner. However, in order to enhance productivity and yield, minimizing the number of photomasks to reduce the number of steps is considered as effective means.
A photomask is used for forming a photoresist pattern to be a mask in an etching step on a substrate in a photolithography technique. When one photomask is used, the steps of coating a resist, pre-baking, light exposure, development, post-baking, and the like, and the steps of forming a coating and etching before and after the steps, and the steps of peeling off a resist, washing, drying and the like are added, which complicates a manufacturing process.
The present invention has been made in view of the above-mentioned background, and an object thereof is to realize the reduction of a manufacturing cost and enhancement of yield by reducing the number of steps of a TFT in an electro-optical device typified by an active matrix liquid crystal display device.
In order to solve the above-mentioned problem, according to the present invention, a TFT is manufactured by using two photomasks. More specifically, a TFT can be formed by using two photomasks: a first photomask for forming a data wiring and a pixel electrode, and a second photomask for forming a gate electrode. A resist pattern formed by using the second photomask is also applied to etching processing of an n-type first semiconductor film, a second semiconductor film for forming a channel, and barrier metal, other than as a gate electrode.
A semiconductor device of the present invention includes: a first wiring and a second wiring formed of a first conductive film on an insulating surface; a first semiconductor film of one conductivity type formed on the first and second wirings so as to correspond thereto; a second semiconductor film formed on upper layer of the first semiconductor film of one conductivity type across the first wiring and the second wiring; an insulating film formed on the second semiconductor film; and a third conductive film formed on the insulating film.
Further, another structure of a semiconductor device of the present invention includes: a first wiring and a second wiring formed of a first conductive film on an insulating surface; a second conductive film formed on the first and second wirings so as to correspond thereto; a first semiconductor film of one conductivity type formed on the second conductive film; a second semiconductor film formed on an upper layer of the first semiconductor film of one conductivity type across the first wiring and the second wiring; an insulating film formed on the second semiconductor film; and a third conductive film formed on the insulating film, characterized in that an end portion of the second semiconductor film is provided inside an end portion of the second conductive film.
Furthermore, another structure of a semiconductor device of the present invention includes: a data wiring and a pixel electrode formed on an insulating surface; a first semiconductor film of one conductivity type formed so as to correspond to the data wiring and the pixel electrode; a second semiconductor film formed on an upper layer of the first semiconductor film of one conductivity type across the data wiring and the pixel electrode; a gate insulating film formed on the second semiconductor film; and a gate electrode formed on the gate insulating film.
Moreover, another structure of a semiconductor device of the present invention includes: a data wiring and a pixel electrode formed on an insulating surface; barrier metal formed so as to correspond to the data wiring and the pixel electrode; a first semiconductor film of one conductivity type formed on the barrier metal; a second semiconductor film formed on an upper layer of the first semiconductor film of one conductivity type across the data wiring and the pixel electrode; a gate insulating film formed on the second semiconductor film; and a gate electrode formed on the gate insulating film, characterized in that an end portion of the second semiconductor film is provided inside an end portion of the barrier metal.
A method of manufacturing a semiconductor device of the present invention by using two photomasks includes the steps of: forming a first mask by first light exposure, using a first photomask; etching a first semiconductor film of one conductivity type, a second conductive film, and a first conductive film by first etching processing, using the first mask; forming a second mask by second light exposure, using a second photomask; etching a third conductive film by second etching processing, using the second mask; and etching an insulating film, a second semiconductor film, the first semiconductor film, and the second conductive film by third etching processing after the second etching processing.
Furthermore, another structure of a method of manufacturing a semiconductor device of the present invention includes the steps of: forming a first conductive film on an insulating surface; forming a second conductive film on the first conductive film; forming a first semiconductor film of one conductivity type on the second conductive film; forming a first mask by first light exposure using a first photomask; first etching of etching the first semiconductor film of one conductivity type, the second conductive film, and the first conductive film by first etching processing, using the first mask; forming a second semiconductor film after the first etching step; forming an insulating film on the second semiconductor film; forming a third conductive film on the insulating film; forming a second mask by second light exposure using a second photomask; second etching of etching the third conductive film by second etching processing, using the second mask; and third etching of etching the insulating film, the second semiconductor film, the first semiconductor film, and the second conductive film by third etching processing after the second etching step.
According to the present invention, a TFT can be formed by using two photomasks, and an electro-optical device typified by an active matrix liquid crystal display device can be manufactured by using the TFT.